1. Field of the Invention
The present invention relates to a dielectric composition able to be used for example for dielectric layers of a multilayer ceramic capacitor and a method of production of the same and to an electronic device using this dielectric ceramic composition for dielectric layers.
2. Description of the Related Art
In recent years, as dielectric ceramic compositions for forming multilayer ceramic capacitors etc., an example of an electronic device, various proposals have been made for the use of inexpensive base metals (for example, nickel, copper, etc.) for the materials for the internal electrodes (see Japanese Patent Publication (A) No. 11-224827, Japanese Patent Publication (A) No. 60-131708, Japanese Patent Publication (B) No. 57-37081, and Japanese Patent Publication (A) No. 63-126117).
However, in each of these dielectric ceramic compositions, the low frequency dielectric characteristic after firing deteriorated (change in capacity, dielectric loss) or the accelerated lifetime of the insulation resistance after firing became shorter. Therefore, when using a dielectric ceramic composition to produce a multilayer ceramic capacitor having nickel or other base metal internal electrodes, the reliability of the multilayer ceramic capacitor obtained tended to fall.
Therefore, various proposals have been made to maintain the superior low temperature dielectric characteristic, increase the accelerated lifetime of the insulation resistance of dielectric ceramic compositions, and improve the reliability of multilayer ceramic capacitors using such dielectric ceramic compositions (for example, see Japanese Patent Publication (A) No. 2002-80278, Japanese Patent No. 2997236, and WO02/00568).
Japanese Patent Publication (A) No. 2002-80278 discloses a dielectric ceramic composition having a dielectric oxide of a composition expressed by (Ca1-xSrx)m.(Zr1-yTix)O3 (where, 0.995≦m<1.08, 0≦x≦1.00, 0.8≦y≦1.00) as its main component and containing, with respect to 100 moles of the main component, 0.01 to 2 moles (however, excluding 2 moles) of at least one type of oxide of V, Nb, W, Ta, and Mo, less than 4 moles of MnO2, and less than 15 moles of at least one compound of SiO2, MO (where M is at least one type of element selected from Ba, Ca, Sr and Mg), Li2O, and B2O3.
Japanese Patent No. 2997236 discloses a dielectric ceramic composition having a dielectric oxide of a composition expressed by (Ca1-xSrx)m.(Z1-yTiy)O3 (where, 0.75≦m≦1.04, 0≦x≦1.00, 0≦y≦0.1) as its main component and containing, with respect to 100 moles of the main component, at least one type of oxide of Nb, W, Ta, and Mo, but not V, 0.1 to 10 moles of Al2O3, 0.2 to 5 moles of MnO2, and 0.5 to 15 moles of a compound oxide of Ba, Ca, and Si.
WO02/00568 discloses a dielectric ceramic composition having a dielectric oxide of a composition expressed by (Ca1-xSrx)m.(Zr1-yTiy)O3 (where, 0.8≦m<1.3, 0≦x≦1.00, 0.1≦y≦0.8) as its main component and containing, with respect to 100 moles of the main component, 0.01 to 5 moles of at least one type of oxide of V, Nb, W, Tag and Mo, 0.2 to 5 moles of MnO2, and less than 15 moles of at least one compound of SiO2, MO (where X is at least one type of element selected from Ba, Ca, Sr, and Mg), Li2O, and B2O3.
However, even with the dielectric ceramic compositions described in Japanese Patent Publication (A) No. 2002-80278, Japanese Patent No. 2997236, and WO02/00568, a sufficient accelerated lifetime of insulation resistance is sometimes still not obtained. As a result, when using a dielectric ceramic composition to produce a multilayer ceramic capacitor having nickel or other base metal internal electrodes, it is not possible to improve the reliability of a multilayer ceramic capacitor.
Note that this type of dielectric ceramic composition, as explained above, generally is comprised of a main component comprised of a CaSrZrTi-based or other dielectric oxide and subcomponents comprised of various oxides.
In the past, for the purpose of improving the various characteristics of dielectric ceramic compositions, the timing of adding the above subcomponents in the process of production of a dielectric ceramic composition has been studied. Explaining the timing of addition, it may be roughly divided into so-called “pre-addition” and “post-addition”. Here, “pre-addition” is the method of weighing and mixing starting materials for obtaining the dielectric oxide for forming the main component (if taking as an example Japanese Patent Publication (A) No. 2002-80278, Japanese Patent No. 2997236, and WO02/00568, the dielectric oxides expressed by (Ca1-xSrx)m.(Zr1-yTiy)O3) after firing (for example, CaCO3, SrCO3, TiO2, and ZrO2) and the various compounds for forming the subcomponents (if taking as an example Japanese Patent Publication (A) No. 2002-80278, at least one type of oxide of V, Nb, W, Ta; and Mo, MnCO3, SiO2, etc.) after firing in accordance with the final composition targeted, calcining the result to obtain a calcined material, then firing the dielectric material formed by only this. The “post-addition” is the method of weighing and mixing starting materials for obtaining the dielectric oxide for forming the main component after firing in accordance with the final composition targeted, calcining the result to obtain the calcined material, then adding the various compounds for forming the subcomponents after firing and firing the dielectric material formed by the mixture of the calcined material and various compounds obtained.
In the past, it had been thought that the compositions or weights of the subcomponents added to the main component themselves affected the characteristics of the dielectric ceramic composition. The timing of addition of the subcomponents had not been particularly considered. Therefore, the method based on the simplest form of pre-addition had been adopted (see Japanese Patent Publication (A) No. 8-8137). After this, the timing of addition of the subcomponents came to be considered as an important factor together with the compositions and amounts of the subcomponents added. In recent years, methods based on post-addition were proposed for several compositions (see Japanese Patent Publication (A) No. 2001-97772 and Japanese Patent Publication (A) No. 2003-146748). Further, the method of mixing part of the subcomponents when producing the main component and adding the remaining subcomponents to the obtained calcined material has also been proposed (see Japanese Patent Publication (A) No. 2000-223349 and Japanese Patent Publication (A) No. 2002-80279).
However, whether the method based on pre-addition of the subcomponents is suitable or the method based on post-addition of all or part of the subcomponents is suitable has to be confirmed by experiment for each target composition. Even a person skilled in the art would find it difficult to determine which method is suitable for systems of different compositions without actual confirming experiments.